1. Field of the Invention
The present invention relates to a method for counteracting the curling tendency of gas barrier film, and to a method for producing a gas barrier film that includes the method for counteracting the curling tendency of gas barrier film. The invention also relates to a gas barrier film to which is applied the method for counteracting the curling tendency of gas barrier film, and to a method for producing an electronic device that comprises using the gas barrier film produced according to the method for producing gas barrier film.
2. Description of the Related Art
It is known that when a rolled film or sheet is stored as such, it will gain a tendency to curl up. The rolled film or sheet thus having the curling tendency will still keep its curling tendency even after cut, therefore bringing about a problem in that the transferability and the pileup capability of the cut films or sheets would worsen. Some methods have heretofore been known for counteracting the curling tendency of such films and sheets thus having gained the tendency to curl up, for example, as in JP-A 2001-226009 and 6-64145.
JP-A 2001-226009 discloses a method for counteracting the curling tendency of roll paper of a rolled sheet by the use of a hot roller, wherein the heating temperature of the hot roller and the lapping time of the sheet around the peripheral surface of the hot roller are specifically defined, based on the curling information of the sheet.
However, the reference does not concretely disclose the temperature at which the rolled sheet is heated, and in addition, in this, the curling tendency of the rolled sheet is counteracted by lapping it around the hot roller in the same direction as the curling direction of the sheet, and therefore, the curling tendency counteracting effect is insufficient. Further, according to the method described in the reference, the entire surface of the rolled sheet is kept in close contact with the peripheral surface of the hot roller for counteracting the curling tendency of the sheet, and therefore, according to the constitution of the apparatus described in the reference, the roll for rewinding up the sheet therearound in the direction to the side opposite to the side thereof heated by the hot roller is located considerably posteriorly from the hot roller. Therefore, according to the curling tendency counteracting method, the sheet, after heated, shall take a long period of time before it is rewound up in the direction to the side opposite to the heated side thereof.
JP-A 6-64145 discloses a method for counteracting the curling tendency of an original fabric not damaging the surface of the fabric, wherein a small-diameter roller is used as a curling tendency-counteracting roller and wherein the roller is heated up to a temperature corresponding to the winding core diameter of the feed roll from which the original fabric is fed and then the original fabric is wound around the roller under tension in the direction opposite to the winding direction around the feed roll. This reference discloses that the optimum heating temperature in the case where the winding core of the feed roll is 200 mm is incidentally 80° C. that corresponds to the glass transition temperature of polyethylene terephthalate of the original fabric.
However, this reference discloses that, for feed rolls having a different winding core diameter, the optimum heating temperature is lower than the glass transition temperature of the original fabric, but this does not suggest that heating the original fabric up to a temperature not lower than the glass transition temperature thereof would be preferable. In addition, in this reference, the curling tendency counteracting roller is kept in close contact with the entire surface of the original fabric for counteracting the curling tendency of the fabric.
On the other hand, regarding a gas barrier film having a gas barrier layer, when a gas barrier film having gained a tendency to curl up is cut as such into a sheet and when the sheet is stuck to the substrate having electronic elements mounted thereon, then the curling level of the sheet resulting from the curling tendency thereof is often problematic. Concretely, when electronic elements are sealed up with a gas barrier film, then there may occur a problem in that the gas barrier film itself could not adhere to the substrate, or there may occur a trouble in that the gas barrier film stuck to the substrate would peel away from the substrate with time. Regarding the gas barrier film, the adhesiveness thereof to the substrate may have a direct influence on the gas barrier property of the film, and therefore, the above problems are more serious than those of the curling tendency of other ordinary films.
Recently, the application of gas barrier film to organic EL displays and others is expanding, and it is desired to produce a large amount of more powerful gas barrier film according to a more simplified production method. From this viewpoint, a method is desired for counteracting the curling tendency of gas barrier film within a short period of time not worsening the gas barrier property thereof.
For counteracting the curling tendency of gas barrier film, the present inventors investigated the methods described in JP-A 2001-226009 and 6-64145 and have found that these methods are unsuitable to the case of counteracting the curling tendency of gas barrier film. Concretely, according to the method described in JP-A 2001-226009, the preset temperature range is unclear and, in addition, there still remains a problem in that the curling tendency of the sheet could not be sufficiently counteracted within a short period of time since the sheet is wound around the hot roller for counteracting the curling tendency of the sheet on the side of the support thereof. On the other hand, it has been known that, when the method described in JP-A 6-64145 is applied to a gas barrier film, then the entire surface of the gas barrier film is inevitably kept in direct contact with the curling tendency-counteracting roller therefore resulting in that the gas barrier film may be scratched and the gas barrier property of the film may be worsened. In addition, it has been known that the heating temperature described in that reference is unsatisfactory from the viewpoint of counteracting the curling tendency of the film within a short period of time.